Optical networks communicate information over optical fiber using optical transmitters and optical receivers. The transmitters and receivers may each be implemented with photonic integrated circuits (PICs). A PIC is a device that may integrate multiple photonic functions such as modulation, amplification, power monitoring at multiple optical wavelengths on a single integrated device. PICs may be fabricated in a manner similar to electronic integrated circuits but, depending on the type of PIC, may incorporate one or more types of materials, including silica on silicon, silicon on insulator, various polymers, and semiconductor materials. Typically, semiconductor materials which may be used to make semiconductor lasers, such as III-V or II-VI semiconductor material systems, may be incorporated into the PIC. Such semiconductor materials include, but are not limited to InGaAsP, AlInGaAs, and GaInNAsSb systems. Hybrid PICs are also known that include silicon-based planar lightwave circuits (PLC) and III-V or II-VI based devices. Such hybrid PICs may be realized by transferring an epitaxial layer on a substrate and forming various optical components on the epitaxial layer.
PICs may include multiple optical sources, each of which outputting an optical signal at a corresponding one of a plurality of wavelengths. The optical signals are combined by an optical combiner and then output from the PIC as a wavelength division multiplexed (WDM) signal. The optical signal wavelengths within the WDM signal often conform to a spectral grid or “channel grid”, whereby each wavelength is separated from another by a uniform spacing, e.g., 200 GHz. The International Telecommunications Union (ITU) has recommended a standard set of frequencies (“ITU grid”), which many WDM systems comply with. The channel grid frequencies often match the frequencies on the ITU grid.
One WDM system, however, may use a first subset of ITU grid frequencies, while another WDM system may use a second subset of ITU grid frequencies. Thus, a different PIC is often fabricated for each set of required frequencies. Accordingly, there is a need for PIC having an associated set of wavelengths, or channel grid that may be tuned over a wide spectral range so as to operate at multiple channel grid frequencies. Preferably, performance parameters of the PIC are maintained or exceeded over the tuning range.